Check that kernel source code has extern C defined (AMDResearch#70)

* Verify that kernel code is wrapped in extern C

* Remove curly braces

* Add breakline

* Change raise type

* Fix checks

* Return RunTime error

* Check construct

* Use Syntax error

* Change way we do pytest

* Only check if extern C exists

* Remove unused check

npu/build/kernel.py

@@ -12,6 +12,7 @@
 from .port import BufferPort, RTPPort
 from typing import Optional, Callable, List, Dict
 import re
+import warnings
 
 
 class Kernel(KernelMeta):
@@ -56,6 +57,7 @@ def __init__(self, srccode : str, behavioralfx:Optional[Callable]=None, top_func
 
         self.kb = KernelObjectBuilder(self.ktype, self.srccode, self.srcfile)
         self._main_function_sanity_check()
+        self._extern_c_check()
         self._expose_ports()
 
     def _expose_ports(self)->None:
@@ -96,6 +98,13 @@ def _main_function_sanity_check(self)->None:
         if not self._main_function['rtnType'] == "void":
             raise RuntimeError(f"The return type of the top_level function should be void not {self._main_function['rtnType']}")
 
+    def _extern_c_check(self):
+        """Verify that extern C is used"""
+        tight_code = self.srccode.replace(' ', '').replace('	', '')
+        if 'extern"C"' not in tight_code:
+            raise SyntaxError('extern "C" not found. Top level function '
+                              'should be wrapped by extern "C"')
+
     def display(self)->None:
         """Render the kernel code in a jupyter notebook."""
         from IPython.display import display, Code

tests/test_externc.py

@@ -0,0 +1,27 @@
+# Copyright 2024 Advanced Micro Devices, Inc.
+# SPDX-License-Identifier: MIT
+
+import pytest
+from npu.build.kernel import Kernel
+from npu.lib import Plus1
+
+
+kernel_src = Plus1().srccode
+
+kernel_src1 = kernel_src.replace('\n\n}', '')
+
+
+def test_externc_good():
+    krnl_obj = Kernel(kernel_src)
+    krnl_obj.build()
+    assert krnl_obj
+
+
+@pytest.mark.parametrize('replacewith', [''])
+def test_externc_bad(replacewith):
+    src_code = kernel_src1.replace('extern "C" {', replacewith)
+
+    with pytest.raises(SyntaxError) as excinfo:
+        _ = Kernel(src_code)
+
+    assert 'extern "C" not found.' in str(excinfo.value)